OpenRA - open source version of the all time classic C&C Red Alert. OpenRA has a very dynamic community that benefits from a pool of experienced programmers and old game fanatics like myself. The game has been in development the past 3 years but now it has a complete stable version in progress (4-8 weeks) to appeal to a broader group of gamers. The game works well with OS X and Linux.
OpenRA homepage: http://openra.res0l.net/ https://github.com/OpenRA/OpenRA/
Here is the latest gameplay video of the latest release: https://www.youtube.com/watch?v=ISMw9hmLHFQ
I would love to see this game reviewed on this site sometime.